Arrow of time

[Greg Boyles]

nowhere.

 

 

You already lost me. If I defined "move" I would maybe say "a change of position over time" or, perhaps better put "a change of position between two times". That definition, however, doesn't work if you say "moving through time".

 

With my definition of "move", if you say "moving through time" you are literally saying "a change of position between two times through time". I can't make any sense of that so I don't know what "move through time" means.

 

This does all seem rather off topic.

 

 

My original most was about the arrow of time.

 

 

Some one's argument was that time does not flow and therefore does not have an arrow.

 

 

I came up with the ruler analogy for time where we change our position and time cordinate rather than time flowing around us - it was accepted.

 

Makes sense since time is supposed to be a dimension according to relativity.

 

 

But I still don't see how this scheme precludes an arrow. I.E. We can only increase our time coordinate but not decrease. We can't move back in time and therefore time still has an arrow - into the future only.

[swansont]

Time as a dimension is not really a construct of relativity — the concept is there is Newtonian physics. Relativity showed that time and space are related.

 

So you are stating that

1,1,1,1

and

1,1,1,2

are occupied by the same object

 

If I asked you are coordinates

1,1,1,1

and

2,1,1,1

occupied by the same object?

What would you think? (speaking about point & massive object)

 

Classically, particles/objects can only have one set of spatial coordinates at any time.

[Iggy]

Some one's argument was that time does not flow and therefore does not have an arrow.

I see.

 

The idea of the arrow is that it points one direction or the other. The idea is not that it 'flows' or 'moves'.

 

Think of it this way: if there were a preferred direction in space then everyone, on any planet, any species, would be able to point in that direction and say "that direction is special". That would be an arrow of space.

 

An arrow of time is anything about nature or how the laws of physics work that lets us point to the future or the past and say "that direction is special because..."

[Greg Boyles]

I see.

 

The idea of the arrow is that it points one direction or the other. The idea is not that it 'flows' or 'moves'.

 

Think of it this way: if there were a preferred direction in space then everyone, on any planet, any species, would be able to point in that direction and say "that direction is special". That would be an arrow of space.

 

An arrow of time is anything about nature or how the laws of physics work that lets us point to the future or the past and say "that direction is special because..."

 

Well all the evidence around us suggests to me that the direction of the future is indeed special for everyone and everything in the universe, even if we/things may experience different rates of movement into the future due to relativistic effects.

[swansont]

The idea of the arrow is that it points one direction or the other. The idea is not that it 'flows' or 'moves'.

 

I agree they are separate, but I also think it's a matter of taking a metaphor too literally.

[michel123456]

Well, you said that. I was working off your premise, but it's a good premise. I agree. Your car keys are the same yesterday as today... same keys. Ok.

 

 

Now you have the same car keys on the kitchen table and the coffee table at the same time. In my everyday experience, that doesn't happen.

 

In the first question you answered yes.

In the second you answered no.

 

That makes the time coordinate kind of special.

Why do you believe the time coordinate is so special?

 

Because IMHO there is no difference between the 2 questions: time coordinates have nothing "special". IOW an object A can not be both at 1,1,1,1 and at 1,1,1,2, exactly as an object A can not be both at 1,1,1,1 and 2,1,1,1.

 

Sorry Greg if you are feeling we are getting far from the subject, i hope coming back soon closer to the OP.

Edited November 9, 2011 by michel123456

[Iggy]

Well all the evidence around us suggests to me that the direction of the future is indeed special for everyone and everything in the universe...

Right. That would be what wiki calls the "psychological/perceptual arrow of time"

 

In the first question you answered yes.

In the second you answered no.

 

That makes the time coordinate kind of special.

Why do you believe the time coordinate is so special?

 

Because IMHO there is no difference between the 2 questions: time coordinates have nothing "special". IOW an object A can not be both at 1,1,1,1 and at 1,1,1,2, exactly as an object A can not be both at 1,1,1,1 and 2,1,1,1.

Common sense should tell us that an object, like a key, can be at the same spot two different times (yesterday and today, for example) but cannot be at two different spots at the same time. Common sense keys us in on that. edit -> sorry, I should maybe avoid idioms. I noticed you spelled view 'vue' which suggested maybe you speak french natively although your english is fantastic in any case so I maybe shouldn't have thought twice about it... Common sense and experience tells us as much <- edit

 

The laws of mechanics do as well.

Edited November 9, 2011 by Iggy

[michel123456]

Right. That would be what wiki calls the "psychological/perceptual arrow of time"

 

 

Common sense should tell us that an object, like a key, can be at the same spot two different times (yesterday and today, for example) but cannot be at two different spots at the same time. Common sense keys us in on that. edit -> sorry, I should maybe avoid idioms. I noticed you spelled view 'vue' which suggested maybe you speak french natively although your english is fantastic in any case so I maybe shouldn't have thought twice about it... Common sense and experience tells us as much <- edit

 

The laws of mechanics do as well.

 

If you stated that "an object, like a key, can be at the same spot two different times (yesterday or today, for example)" we could get into an agreement.

What I say is : a key can be yesterday OR today, but not today AND yesterday. You have to choose. The key didn't duplicate magically nor entered some "other past universe" in which it got frozen.

 

What the laws of mechanics tell us is that no matter your state on motion, wathever you do, you will observe only one key.

 

And i am fighting common sense.

[Iggy]

If you stated that "an object, like a key, can be at the same spot two different times (yesterday or today, for example)" we could get into an agreement.

What I say is : a key can be yesterday OR today, but not today AND yesterday. You have to choose.

I don't follow. The key was here yesterday. The key is here today. They are both true. And is the logical conjunction.

[michel123456]

I don't follow.

 

I realize that. I guess you are not alone.

Actually I feel alone.

 

It is quite easy to persuade someone that we are translating in time, instead of time flowing over us.

But the next step, that is to consider displacement in time exactly as displacement in space, is not easy at all. People is stuck to the idea that when an object translates in time it leaves its living imprint at each moment. The corresponding concept for those who believe into the "flow of time" corresponds to the machinery of Time extruding matter and energy as much the object gets through it. IMHO it is a wrong concept.

To me, translation in time has no conceptual difference with displacement in space. When an object goes from one point in space to another it does not duplicate. The same goes for time: when an object changes time coordinates, it does not duplicate. So simple.

Edited November 9, 2011 by michel123456

[Iggy]

When an object goes from one point in space to another it does not duplicate.

we already agreed that it is the same object -- not a duplicate.

 

To me, translation in time has no conceptual difference with displacement in space.

But you know from everyday experience that isn't so. You know that the key was here yesterday. You know that it is here today. You want to say "either the key was here yesterday or it is here today", but you must know that isn't true. It is self-evidently false.

[Greg Boyles]

Right. That would be what wiki calls the "psychological/perceptual arrow of time"

 

 

The problem is that I can't see how this phenomenum is simply a psychological construct because there is abundant evidence on erth and throughout the cosmos that it has occured long before there were human minds to create the construct.

[Iggy]

The problem is that I can't see how this phenomenum is simply a psychological construct because there is abundant evidence on erth and throughout the cosmos that it has occured long before there were human minds to create the construct.

Then, if I understand you correctly, you would suspect that there is something about the laws of physics which distinguishes past from future?

[michel123456]

Then, if I understand you correctly, you would suspect that there is something about the laws of physics which distinguishes past from future?

There is something about the Laws of Nature.

And there is something missing in our laws of physics, for sure.

[Greg Boyles]

There is something about the Laws of Nature.

And there is something missing in our laws of physics, for sure.

 

Well entropy for starters.

 

But it is abundantly clear to all, including yourself no doubt, that the physics of the cosmos is far from complete. Relativity and quantum theory are not reconciled for starters.

 

Just because your mathematics may not currently distinguish past from future does not necessarily make it so. It may mean there is something missing from you mathematics.

 

I use the word 'may' deliberately here.

[Iggy]

There is something about the Laws of Nature.

And there is something missing in our laws of physics, for sure.

Well entropy for starters.

I agree.

 

What trips me is thinking that entropy is not time symmetric, but it is nonetheless derived from the equations of motion which are time symmetric. The arrow arises more from the boundary conditions of the system than the underlying physics. I tried to say this earlier in the thread but mangled it horrifically.

 

So I think Michael makes the perfect distinction. It is like the arrow comes more from nature than physics. In other words, it comes more from the initial condition of the universe and not the laws which explain how the system should behave.

 

I could be entirely wrong on this line of thinking.

[Greg Boyles]

I agree.

 

What trips me is thinking that entropy is not time symmetric, but it is nonetheless derived from the equations of motion which are time symmetric. The arrow arises more from the boundary conditions of the system than the underlying physics. I tried to say this earlier in the thread but mangled it horrifically.

 

So I think Michael makes the perfect distinction. It is like the arrow comes more from nature than physics. In other words, it comes more from the initial condition of the universe and not the laws which explain how the system should behave.

 

I could be entirely wrong on this line of thinking.

 

Perhaps the arrow of time/events is an emergent phenomenum of complexity!

[michel123456]

What we call the arrow of time is a phenomena of asymmetry. Out of entropy there are other physical concepts that are non symmetric, we simply tend not to pay attention about it.

For example, distance is a measurement that is always positive by definition. Talking about negative distance is the same insensitive as talking about negative time.

Another example is gravity, which is always positive as far as our direct observations are concerned.

 

That is a good reason IMHO to consider that all those exclusively positive concepts (time, distance, gravity, entropy) should be connected by a single explanation.

[Appolinaria]

How can a key be in the same spot as it was even a second ago, based on the fact that everything in the universe is accelerating from each other, the Earth is rotating, and it all moves across the expanse of the universe?

 

Yes, the key might be in the same spot on the shelf as it was yesterday, but the entire Earth is not going the same speed it was yesterday, nor is Earth in the same place in space as it was yesterday...

[michel123456]

How can a key be in the same spot as it was even a second ago, based on the fact that everything in the universe is accelerating from each other, the Earth is rotating, and it all moves across the expanse of the universe?

 

Yes, the key might be in the same spot on the shelf as it was yesterday, but the entire Earth is not going the same speed it was yesterday, nor is Earth in the same place in space as it was yesterday...

 

True.

The question was not upon that point though.

Maybe it was not even a question but a simple misunderstanding.

What i said was that the key was a single object, statement on which Iggy agreed because he wrote:

we already agreed that it is the same object -- not a duplicate.

 

As a consequence, i stated that the object, the key, changed spacetime coordinates, statement on which I suppose there was no ambiguity.

And as a final consequence, I stated that if there was only one & single object, and that this object changed spacetime coordinates, it could not occupy both coordinates "at the same time".

This last statement introduces a confusion that I am aware of, and Iggy disagrees because I introduced maliciously a fifth dimension.

 

It is a pleasure disagreeing with Iggy because he makes his point clear without shouting.

But we still disagree.

 

As for your remark, it is perfectly correct: a hypothetical time traveler should not only travel through time but also through space.

[MigL]

If I may add something to this discussion. I do believe time has an 'arrow' but I don't think it is due strictly to entropy. Time is different from the spatial dimensions. For the spatial dimensions, what happens at a certain co-ordinate can affect another co-ordinate, no matter where it is. But for time, only what happens in the past can have an effect on the present or the future. The future cannot affect the present or past ( ie. we remember past events but not future ones ). It is this causality effect which determines the so called arrow of time.

 

I believe it was Michel123456 who previously stated that the two choices are either " we are translating in time or time is flowing over us". I believe a third choice would be that, locally anyway, time advances and carries the local now along with it. The local now being represented by the Einstein-Rosen embedding diagram. I am definitely not saying there is a global now, just to be clear, and even the local now is very loosely defined for clarity and simplicity. As time, or the local now moves foreward, another layer or foliation is added and the previous ones become past. These underlying layers can still affect the top-most layer, the present, and so we can remember past events, and there are fossil records and history in general.

[Appolinaria]

Michel, thanks.

If anyone could answer the following layman questions I would really appreciate it.

 

 

If objects in our universe are accelerating away from each other, are they increasing in kinetic energy? Is this why entropy is increasing?

 

Wikipedia says, "Increases in entropy correspond to irreversible changes in a system, because some energy is expended as waste heat, limiting the amount of work a system can do."

 

Is this why there is an arrow of time?

Edited November 12, 2011 by Appolinaria

[michel123456]

If objects in our universe are accelerating away from each other, are they increasing in kinetic energy? Is this why entropy is increasing?[/size][/font]

 

IIRC standard cosmology states that space is expanding at an accelerating rate, not proper motion.

[Appolinaria]

entropy

[IM Egdall]

Perhaps the arrow of time/events is an emergent phenomenum of complexity!

 

I think Iggy hit the nail on the head when he said the arrow of time comes from the initial condition of the universe. As I understand it, the entropy of the universe was lower at its beginning and has been increasing ever since. This, I think, is at the root of the perceived forward arrow of time.

 

But why the initial universe was at lower entropy -- I don't think anyone has an answer for this.

Edited November 12, 2011 by IM Egdall